One of the key components of any computer system is a place to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disk drive. The most basic parts of a disk drive are a disk that is rotated, an actuator that moves a transducer to various locations over the disk, and electrical circuitry that is used to write and read data to and from the disk. The disk drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disk surface. A microprocessor controls most of the operations of the disk drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disk.
The transducer is typically housed within a small ceramic block. The small ceramic block is passed over the disk in a transducing relationship with the disk. The transducer can be used to read information representing data from the disk or write information representing data to the disk. When the disk is operating, the disk is usually spinning at relatively high RPM. These days common rotational speeds are 5100 and 7200 RPM. Rotational speeds of 10,000 RPM and higher are contemplated for the future. These high rotational speeds place the small ceramic block in high air speeds. The small ceramic block, also referred to as a slider, is usually aerodynamically designed so that it flies over the disk. The best performance of the disk drive results when the ceramic block is flown as closely to the surface of the disk as possible. Today's small ceramic block or slider is designed to fly on a very thin layer of gas or air. In operation, the distance between the small ceramic block and the disk is very small. Currently "fly" heights are about 0.0003 mm. In some disk drives, the ceramic block does not fly on a cushion of air but rather passes through a layer of lubricant on the disk.
Information representative of data is stored on the surface of the memory disk. Disk drive systems read and write information stored on tracks on memory disks. Transducers, in the form of read/write heads, located on both sides of the memory disk, read and write information on the memory disks when the transducers are accurately positioned over one of the designated tracks on the surface of the memory disk. The transducer is also said to be moved to a target track. As the memory disk spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the memory disk. Similarly, reading data on a memory disk is accomplished by positioning the read/write head above a target track and reading the stored material on the memory disk. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disk drives, the tracks are a multiplicity of concentric circular tracks. In other disk drives, a continuous spiral is one track on one side of a disk drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
One of the most critical times during the operation of a disk drive is just before the disk drive shuts down. The small ceramic block is typically flying over the disk at a very low height when shutdown occurs. In the past, the small block was moved to a non data area of the disk where it literally landed and skidded to a stop. Problems arise in such a system. When disks were formed with a smooth surface, stiction would result between the small ceramic block and the head. In some instances the force due to stiction was so strong that it virtually ripped the head off the suspension. Amongst the other problems was a limited life of the disk drive. Each time the drive was turned off another start stop contact cycle would result. After many start stop contacts, the small ceramic block may chip or produce particles. The particles could eventually cause the disk drive to fail. When shutting down a disk drive, several steps are taken to help insure that the data on the disk is preserved. In general, the actuator assembly is moved so that the transducers do not land on the portion of the disk that contains data. There are many ways to accomplish this. A ramp on the edge of the disk is one design method that has gained industry favor more recently. Disk drives with ramps are well known in the art. U.S. Pat. No. 4,933,785 issued to Morehouse et al. is one such design. Other disk drive designs having ramps therein are shown in U.S. Pat. Nos. 5,455,723, 5,235,482 and 5,034,837.
Typically, the ramp is positioned to the side of the disk. A portion of the ramp is positioned over the disk itself. In operation, before power is actually shut off, the actuator assembly swings the suspension or another portion of the actuator assembly up the ramp to a park position at the top of the ramp. When the actuator assembly is moved to a position where parts of the suspension are positioned on the top of the ramp, the sliders or ceramic blocks do not contact the disk. Commonly, this procedure is known as unloading the heads. Unloading the heads helps to insure that data on the disk is preserved since, at times, unwanted contact between the slider and the disk results in data loss on the disk. The actuator assembly may be provided with a separate tang associated with each head suspension. The tang may ride up and down the ramp surface. In other drives, the ramp may be positioned such that the suspension rides up and down the ramp to unload and load the disk or disks of the disk drive.
In disk drives having a ramp for loading and unloading the transducing heads from the disk, it is critical to be able to control the friction between the portion of the suspension that rides up the ramp, such as a tang, and the ramp itself. It is also becoming necessary to control the friction such that portions of the ramp, such as the parking detente, have a higher coefficient of friction than other portions of the ramp. Ramps typically have a complex geometry. One commonly used cost effective way to achieve the complex geometry is to use injection molding to form the ramp from a single material. Injection molding typically uses a single polymer material to form the ramp. The surface finish of the ramp is typically controlled by the polymer used for the injection molding the part. Often, the polymer material for a ramp is selected on the basis of its thermal and mechanical stability properties rather than for other properties, such as friction. In other words, the tribology of the ramp part is usually not considered as a factor in selecting the material for injection molding of the ramp. Friction is one of many attributes associated with tribology.
Ramps typically include an inclined surface, and a parking area or detent. There may also a flat surface positioned between the inclined surface and the parking detent. A portion of the suspension, such as a tang, rides up and down the ramp when the transducer attached to the suspension is loaded onto or unloaded from the disk. To reduce wear and to reduce the amount of power associated with moving a slider up and down the ramp, it would be advantageous if the coefficient of friction was low on the inclined and the flat surfaces of the ramp. To keep the slider in its parked position, it would be advantageous if the parking area or detent had a higher coefficient of friction.
Currently it is difficult to control the tribological properties of an injection molded port, much less to control the tribological properties in a first area and a second area of the ramp. As a result, controlling the tribology at various portions of the ramp to achieve a high friction surface area and a low friction surface area is generally not considered in the molding process. Therefore, there is a problem associated with making a ramp which has a low friction surface and a higher friction surface within the limits imposed by the polymer materials and the injection molding fabrication processes currently being used.
There is a need for a ramp having a structure that prevents stiction between the suspension and the ramp. There is also a need for a ramp that has a first surface having a first coefficient of friction and a second surface having a second coefficient of friction. There is a need for a method of manufacturing a structure having a first surface having a first coefficient of friction and a second surface having a second coefficient of friction. Furthermore, there is a need for a structure that can be formed using the injection molding process. There is a need for an injection molding process and method in which the friction on the surface of a ramp used in a disk drive can be controlled without compromising the mechanical strength and integrity of the ramp. In addition, there is a need for a ramp that has the necessary thermal properties to undergo repeated thermal cycling in a disk drive. Furthermore, there is a need to have a ramp which can be made of proven materials which have very little or essentially no outgassing which would produce contaminants within the disk drive enclosure.